Investigating the Effect of Light Intensity - PowerPoint.ppt

biology

1. AQA GCSE Combined Science
Investigating the effect of light
intensity on the rate of photosynthesis
in pondweed

2. •To collect a full set of results for 5 different light intensities.
•To calculate the mean number of bubbles for the different light
intensities
•To draw a suitable graph from the results collected
To investigate the effect of light intensity on the rate of photosynthesis
Learning Objective
Success Criteria

3. Photosynthesis is…
‘the process by which plants produce their
own food in the form of glucose.’
Photosynthesis: What Do You
Know?
The equation for photosynthesis is…
Carbon dioxide + water Glucose +
Oxygen
Extension;
Write the balanced symbol equation
6CO
2
+ 6H
2
O C
6
H
12
0
6
+ 6O
2

4. Light Intensity
The amount of light a plant
receives affects the rate of
photosynthesis. If a plant receives
lots of light, lots of photosynthesis
will occur. If there is very little or
no light photosynthesis will stop.
We are going to investigate the
effect of light intensity on the rate
of photosynthesis in pondweed.

5. The Experiment
Investigating the Effect of light
intensity on the Rate of
Photosynthesis

6. How will you be able to
measure this increase??
Prediction
What will happen as the light
intensity the plant receives
becomes greater and greater?
?

7. Prediction
As the light intensity increases the rate
of photosynthesis will also increase.
When a plant is photosynthesising,
bubbles of oxygen will be visible; it is
possible to count these bubbles for a
given amount of time to compare the
effect of light intensity on the rate
of photosynthesis.

8. Equipment List
Risk assessment – please read before collecting your equipment.
10cm piece of Cabomba or Elodea
Paper clip - to weigh down the pondweed
Boiling tube - to place the pondweed in
Metre Rule - to measure accurately the distances
between pondweed and light source
Stop watch - to accurately time 1 minute
Clamp stand - to hold the boiling tube
Lamp - LED light source is best
0.2% solution of sodium hydrogen carbonate
25cm
3
Measuring Cylinder - to measure 20cm
3
hydrogen
carbonate solution

9. Risk Assessment
Hazard Risk
Emergency
Procedure
Lamp near
water
Electric
shock
Inform teacher
immediately
Glassware
(breakages)
Cuts
Apply pressure to the
wound and inform
the teacher

10. Method
Measure 20cm
3
of
sodium hydrogen
carbonate solution
and pour into a
boiling tube.
1 Collect a 10cm piece
of pondweed and
gently attach a
paper clip to one
end.
Clamp the boiling
tube, ensuring light
will be able to be
shone onto the
pondweed.
2 3
Place a metre rule
next to the clamp
stand.
Place the lamp 10cm
away from the
pondweed.
Wait 2 minutes,
until the
pondweed has
started to
produce bubbles.
4 5 6
Using the stopwatch
count the number of
bubbles produced in
a minute.
Repeat stages 5 to 7,
moving the lamp
10cm further away
from the pondweed
each time until you
have 5 different
distances.
Now repeat the
experiment twice
more to ensure you
have 3 readings for
each distance.
7 8 9

11. Diagram

12. https://www.youtube.com/watch?v=cmwOFn67Jqg

13. Recording Results
Distance from
lamp to
pondweed
(cm)
Number of bubbles per minute
Attempt 1 Attempt 2 Attempt 3 Mean
10
20
30
40
50

14. Calculating Mean
To calculate the mean:
•Remember to check for any anomalies in your results.
•If there is an anomaly discard it and do not add it
to your total
Mean =
Total number of bubbles
number of attempts

15. Choose suitable scales and labels for the
axes.
Hint: look at the range of your data.
Decide what type of graph you will plot.
Hint: is your data continuous or
categorical?
Draw a line of best
fit.
Plotting a Graph (Use Graph Paper)

16. Conclusion
What was the effect of
light intensity on the rate
of photosynthesis?
?
Remember to use
examples from your
results to support your
answer.

17. Evaluation
How confident are you that your conclusion is valid?
Most experiments have some errors or encounter
some problems. What was the biggest error or
problem with your experiment and how would you
try to overcome it?
What would be the advantages of comparing your
results with the results of others?
One of the problems with this experiment is that the
lamp can heat up the water in the test tube.
Suggest how this problem can be overcome.

18. Variables
What were the variables in this experiment?
The independent variable was…
The dependent variable was…
The control variables were…

19. Variables Answers
What were the variables in this experiment?
The independent variable was the light intensity
The dependent variable was the amount of bubbles
produced
The control variables were, same amount of time,
same amount of pondweed.

20. Plenary: Change the World
How could what you have learnt today
change the world?
Discuss your ideas with a partner